n. 1. GAME The best and most popular x-box game. Made by Bungie.
2. RELIGIOUS OBJECT a glowing ring of light surrounding Bible-era religious figures. 3. MILITARY A high altitude/low opening parachute jump, where a jumper exits the plane at around 30,000 feet and opens at around 1,000.

Let's go play Halo for 7 hours at a sleepover!

Your halos are glowing so brightly we won't need the lamps, that's very nice.

1) bright glowing ring above the head of religious figures
2)a game for xbox and later PC made by bungie; considered by some to be the best game available on xbox
3) military parachute jump (hi altitude, low opening)

master chief jumping from a plane with a ring above his head would satisfy all three

A religious symbol ussually associated with the Bible and commonly used in paintings in the medieval era of saints etc.
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A First Person Shooter for Xbox with an strong storyline, amusing physics, great multiplayer, and great controls. Slightly overrated.

The young girls heart was so pure you could practically see a halo over her head.

1. A disk (or a ring, more recently) above one's head, usually used in religious context. A halo usually indicates that the one below the halo is a good person.

2. A video game series developed by Bungie Studios, starting with Halo: Combat Evolved back in 2001. Combat Evolved is widely recognized as the game that single-handedly brought attention to the Xbox. Halos 2 and 3, released in 2004 and 2007, respectively, were very well received.
The series' popularity led to two spin-off games, Halo Wars, developed by Ensemble Studios rather than Bungie, and Halo 3: ODST, essentially a filler for the time between Halo 3's release in '07 and Halo: Reach, a game set to be released in 2010. Since Halo 2, Halo's online multiplayer has been incredibly well-received by anyone who doesn't have a shit connection.
Many gamers think Halo is an overrated and generic FPS. Generally, the rest seem to think that Halo is the greatest thing ever to grace their souls. There is an equilibrium, which is the reasonable players who feel that enjoying one game does not make you 100% exclusive.

Just because Halo fanboys can be insufferable, doesn't mean the game is shit. Any reasonable person wouldn't call the game anything short of amazing.
Remember kids, Urban Dictionary is a place for definitions, not slander or favoritism.